The present invention relates to a semiconductor integrated circuit device (which will be referred to as an "IC") which includes a unit cell forming an input/output circuit portion capable of selecting any of a plurality of different input and output functions by changing a wiring pattern, and to a method of fabricating the same. More particularly, the present invention relates to a logic IC resorting to a master slice approach.
For example, a logic IC for a computer adopts the so-called "master slice approach" as its design because it is necessary to design a few, but multiple, kinds of ICs within a short time period. The IC resorting to the master slice approach has an advantage that it can realize a multiplicity of logic functions by providing various wiring patterns for the master, without changing the basic design (i.e., the master). In order to enjoy this advantage, it is necessary that the functions of respective pins (or leads) can be arbitrarily selected or changed so as to satisfy the various requirements. Specifically, it is required that the respective pins can be set so that in the master slice any one function can be arbitrarily selected from the respective functions of an input, an output and bidirectionally of the input and output.
In order to satisfy this requirement, according to the prior art, there is adopted means for providing one I/O cell for each of the bonding pads which are provided for each pin. Here, the I/O cell is a cell (i.e., a unit circuit portion) which is so basically designed (or mastered) that it can be used to construct circuits requiring the largest number of the elements for the respective input and output circuits. In case the aforementioned requirements are to be satisfied by providing such I/O cells, this I/O cell is so formed that it can set the function of one pad (or pin) at any of the input, the output, or bi-directionally of the input and output so as to fabricate the IC resorting to the master slice approach. As a result, the other elements for realizing functions other than the selected one, are not used, but one I/O cell performs nothing but one selected function. Moreover, in the relationship in the arrangement between the conventional bonding pad and this I/O cell, according to the prior art, although the input circuit and the output circuit can naturally be simultaneously constructed using the I/O cell independently of each other, both the input and output cannot be extracted separately and independently of each other, but only either of them can be extracted from the single I/O cell. With this in mind, we, the Inventors, have investigated and revealed that the approach thus far described, i.e., the conventional master slice approach, in which the requirement for setting the functions of the pins is to be satisfied by providing one I/O cell for each one pad, has failed to increase the multiple functions and kinds without changing the basic design.